Study On Rheology Constitutive Model For Structural Soft Clay And Its Application

Nowadays,many reclamation projects are implemented in the coastal areas where all types of soft clays are widely distributed,and the clays bring a lot of environmental problems and geological disasters,such as,engineering-related settlement,deformation of deep foundation pit and its environmental influences,corrosion of structures in salty soils,soft soil foundation treatment and reinforcement,soft soil settlement under seismic load,and so on.A large number of research and practice indicate that those problems are mainly caused by the rheology of soft clays,and especially for the foundation on the newly reclamed soils.Therefore,it is very important for structural designer and constructor to accurately predict and analyze the settlement its influence on the structures,numerical simulation methods are usually needed during this process.It is a key point to select a reasonable rheological constitutive model for the numerical simulation.To solve those problems,fisrstly a large number of experimental data in many related literatures is searched,then,a rheological constitutive model for constitutive soft clay is developed.According to the model,a program is developed based on ABAQUS's UMAT,and using this program several projects are simulated to evaluate the influence of rheology on the structures,and some suggestions are made for the designs and constructions of the structures.The main work and achievements of this thesis are as follows:(1)The changing patterns of viscosity coefficient with time are studied.The expression of viscosity coefficient is developed and its extensive applicability is also verified by a large number of data.The study shows the viscosity coefficient depends on time,confining stresses and deviatoric stresses.After analyzing the mechanism,we believe that the value of viscosity coefficient reflects the thickness of bound water membrane.With the increasement of consolidation pressure,free water and osmotic bound water is drained away,and the thickness of bound water membrane decreases.Therefore,the bonding forces between soil particles increase,which results in the incresement of viscosity coefficient.(2)The rheological constitutive model with two parameters for remolded soils is developed based on the study on viscosity coefficient.Furthermore,the model is substituted by a better one with four parameters.Since the coefficient is function of deviatoric stresses,confining stresses and time,the model can accurately reflects the rheological behavior of soft clay.Then the model is verified to be reasonable and generally applicable.(3)The rheological constitutive model for structured soft clay is developed based on the model for remolded soil.The model can reflect the influence of deviatoric stresses and confining stresses on rheology,and it can perfectly characterize the rheological behavior.Moreover,the model can be conveniently extended to 3D because of its simple form and fewerparamters.(4)The one dimensional constitutive equation for structural soft soil is extended to three dimensions.Based on it the user program ABAQUS is written.The finite element model is developed to calculate the settlement of soft clay in a real project,which is compared wih the experimental data,and the results show the correctness and availability of program and the rheological constitutive model.(5)Based on program,three finite element models reanalyzed,in which the rheology of soft soil effects on the settlement and internal force of the superstructure in frame structure are studies.The results indicate that the total settlement and differential settlement decrease when the stiffness of foundation increases.For structures with isolated footing,the differential settlement leads to the increase of axial forces by 3.24%for the middle columns and the decrease of that by 4.99%for the side columns and corner columns,and the differential settlement results in the decrease of end moments in beams by 10%,and also the increase of mid-span moment.For structures with raft footing,the amplitude of change is smaller.(6)According to the research,some suggestions are given for the design and construction of structures in coastal region to assure the safety and serviceability of structures.